Low-Salt Diets Reduce Heart Disease Risk, Right? A Study Disagrees

The government’s recent Dietary Guidelines for Americans had some familiar recommendations for health: eat more fruits and vegetables, exercise more and lower the amount of salt you eat.

Now a new study from Europe challenges that last piece of advice by suggesting that reducing dietary salt may not benefit your heart health after all. Previous studies have shown that people with high blood pressure can lower their risk of developing hypertension and heart disease by eating less salt. But in the new study, people who had the most salt in their diets actually had the lowest risk of dying from heart disease.

Yes, that’s right. The study involved 3,681 people without heart problems, most of whom also had normal blood pressure. Reporting in the Journal of the American Medical Association (JAMA), the researchers found that those with the highest levels of sodium in their urine (the most accurate way to measure how much salt a person consumes) were more than four times less likely to die from heart disease than those with the lowest intake of sodium. During the nearly eight years of follow up, the heart-related death rate was 0.8% among those with the highest sodium levels and 4% among those with the lowest levels.

“Yes, the findings surprised me and those of us at the American Heart Association (AHA),” says Dr. Ralph Sacco, president of the AHA and chairman of neurology at University of Miami. The AHA is hoping to get Americans to lower their sodium intake to 1,500 mg per day by 2020, far below the 2,300 mg daily maximum that the U.S. Department of Agriculture now advises.

“We have to remember that many people are at high risk for high blood pressure,” says Sacco. “And when we start going up in age, the proportion of people with high blood pressure approaches 70% to 80% or more, so your lifetime risk of high blood pressure is exceedingly high.”

Salt can play a role in blood pressure, and the current study confirmed this, finding that the systolic pressure (the upper number in the blood pressure reading) was slightly higher among those consuming the most salt, compared with those consuming the least. Even so, those people were at no higher risk of developing hypertension.

The current study fuels the brewing debate over whether low-salt standards should apply equally to everyone. Some experts suggest that certain people may be more sensitive to salt than others, or that people with normal blood pressure may not benefit from lowering their sodium intake. Most of the gold-standard studies on salt — in which people are randomly assigned to consume diets high or low in sodium — have involved people who either have hypertension or are at high risk of developing it. Based on that data, scientists just assumed that the same low-salt principle would benefit people at lower risk as well.

But as one of the study authors, Dr. Jan Staessen, professor of medicine at University of Leuven in Belgium, told JAMA in a Q&A, “If you decrease sodium intake a lot, you activate some of the systems that conserve sodium and they are known to have a negative influence on cardiovascular outcomes.” While it’s not know if this is indeed the reason for the contrary findings, it could explain why lower sodium levels were linked to greater heart problems in the trial.

Still, Sacco, as well as the authors, acknowledge that there might be other reasons for the surprising results. First, the study population was relatively young on the whole (participants’ ages ranged from 20 to over 60), and therefore at lower risk of hypertension than an older population. The impact that sodium can have on the heart may differ depending on age.

Second, the scientists took only one urinary sodium reading over a 24-hour period from each participant, and such readings can vary; an average of several measurements might have more accurately captured the participants’ true sodium intake.

And, finally, given the young age of the volunteers, an eight-year follow up may not have been long enough to capture the full risk of heart events or death from heart attacks, which tend to occur in advanced middle age and later.

It appears that the question about how salt affects heart risk is a complicated one. There is certainly strong and undisputed evidence that people with high blood pressure can lower their readings by reducing their salt intake. So it would stand to reason that the same applies to healthy people with normal blood pressure — even if there isn’t the gold-standard scientific evidence to support that.

Of course, dropping blood pressure too low comes with its own health risks — dizziness, fainting and even shock — but most U.S. adults aren’t at risk of hypotension. Sacco points out also that because high blood pressure is associated with both age and obesity, there’s good reason for large swaths of the American public to hold off on the sodium.

“Our population is aging, and more and more people are obese, and less physically active, so we felt that [the AHA’s] recommendation for all Americans to lower their salt intake is important because a large proportion of Americans are intermediate to high risk for developing high blood pressure,” he says. “One study should not change all the other great evidence out there that says we should be lowering sodium. Lowering blood pressure even by a few millimeters can have an impact over a lifetime. So don’t reach for that salt shaker.”